"So is Facebook the location platform now? And is Foursquare an app on that platform?"

His answer (highlights in bold):

No, we're still a platform for location, specifically around sharing locations though check-ins, surfacing interesting things around you and using game mechanics to encourage and reward for certain actions and/or behaviors.

Facebook also launched a location platform, which appears to be mostly based on checkins (and common FB elements like comments / likes / photos)

We already allow users to publish their 4SQ checkins into the Facebook News Feed and we'll eventually going to allow users to push them into the Facebook Checkin Feed. I'd imagine we'll prob pull FB checkins into 4SQ too. We're in the middle of a redesign and some new feature launches, so we're going to get thru those before getting started on FB integration.

Because of Facebook's scale, Facebook Places will be bigger than Foursquare. Facebook Photos is bigger than Flickr. This doesn't mean Foursquare is dead.

Because of this scale, independent developers will probably look to Facebook first when integrating location data. (Foursquare has Facebook Connect integrated onto its Web site for the same reason – scale.)

BUT If Facebook can push to Foursquare, then the Facebook News Feed will only help Foursquare grow.

AND Foursquare is closer to developing a real coupon business.

SO if Foursquare can find a way to share a cut of that business with the appsmakers who "refer" check-ins, then that will encourage developers to stick with Foursquare.